Patch-specific spawning is linked to restoration of a sediment-disturbed lowland river, south-eastern Australia

Landscape-scale, terrestrial modifications of catchments can increase river sediment loads. In some rivers, the development of ‘sand-slugs’ (i.e. discrete slugs of travelling sand particles) subsequently alters habitat structure with links to declines in regional fish diversity. Increasingly, river channel restoration is being used to conserve biodiversity in sediment-disturbed rivers, but there are few examples to guide restoration efforts. In particular, few studies examine the effect of restoration on ecological processes such as spawning. We report on a trial restoration procedure, consisting of sediment extraction and woody debris replacement undertaken in two 1500 m reaches of the Glenelg River, south-eastern Australia. We aimed to examine the association between reach-scale restoration and fish spawning, predicting that reconstructed channel types (pools and runs) would be used more frequently than corresponding un-modified channel types for spawning. Artificial (polyvinylchloride (PVC) tubes) and natural (small woody debris) spawning substrates were used to examine the association of fish spawning with reach and channel type. Restoration increased wood volume, but only increased average run depth at one reach. Species including Gadopsis marmoratus, Philypnodon grandiceps, Hypseleotris spp., Nannoperca variegata and Cherax destructor were observed within spawning substrates, but only P. grandiceps frequently spawned on PVC tubes and sparsely on small woody debris substrates. Spawning frequency varied between reach and channel types, with pools in both restored and un-manipulated reaches used more frequently than runs. Restored pools were less frequently used than un-manipulated pools, but restored runs were used up to 6 times more frequently than un-manipulated runs, indicating that restoration of the shallowest parts of the channel increased spawning opportunities for P. grandiceps. This type of channel restoration may facilitate ecological processes that underpin the persistence of riverine fish populations.